DESCRIPTION: Our recent breakthroughs in applying single B-cell probing and cloning technologies to isolate human antibodies capable of potently and broadly neutralizing HIV-1 primary isolates, along with others, have demonstrated the ability of human B-cell system to generate effective immunity against the virus. To progress on this encouraging discovery and unearth mechanisms by which broadly neutralizing antibodies (bnAbs) could be elicited by immunization, we are challenged by two unsolved and fundamental immunological questions: what are the naive and/or founder (n/f) B-cells and their B-cell receptor (BCR) sequences that must be immunologically selected to generate anti-HIV-1 bnAbs, and how do these selected n/f BCRs react with the HIV-1 envelope (Env) antigen? Having access to precious longitudinal samples from both SHIV-infected rhesus macaques (including lymph nodes) and HIV-1- infected seroconverters, we have a unique opportunity to address these questions by identifying the n/f BCRs responsible for bnAbs and determining their reactivity to the Env antigen. In addition to single B-cell analysis, we have also pioneered the application of deep sequencing technology to mine anti-HIV-1 bnAbs of the whole antibody repertoire. With the aid of these advanced technologies that offer high- resolution analysis of both single and high-number (millions) B-cells, it is feasible to track bnAb responses, thereby catapulting our quest to identiy bnAb-corresponding n/f BCRs. Furthermore, we will isolate the autologous infecting HIV-1 Envs and investigate their reactivity with the n/f BCRs of interest. We will test the hypotheses that n/ BCRs that give rise to bnAbs in SHIV-infected rhesus macaques and HIV-1-infected humans can be identified by deep sequencing of the subject antibodyome from longitudinally collected blood and lymph node cells, and that the n/f BCRs recognize the autologous infecting HIV-1 Envs. If successful, this project will delineate a complex and lengthy B-cell immunological process, revealing the much anticipated initial steps that the HIV-1 Env antigen must take to initiate an effective antibody response. This project will also generate a panel of bnAb-corresponding n/f BCRs that would be invaluable for immunogen screening and may also identify HIV-1 Envs that have the potential to prime these n/f BCRs.